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Journal of Virology, December 2002, p. 12663-12675, Vol. 76, No. 24
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.24.12663-12675.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

In Vitro Activity of the Baculovirus Late Expression Factor LEF-5

Linda A. Guarino,1,2* Wen Dong,2 and Jianping Jin1

Departments of Biochemistry and Biophysics,1 Entomology, Texas A&M University, College Station, Texas 77843-21282

Received 28 June 2002/ Accepted 5 September 2002

The baculovirus late expression factor LEF-5 has a zinc ribbon that is homologous to a domain in the eukaryotic transcription elongation factor SII. To determine whether LEF-5 is an elongation factor, we purified it from a bacterial overexpression system and added it to purified baculovirus RNA polymerase. LEF-5 increased transcription from both late and very late viral promoters. Two acidic residues within the zinc ribbon were essential for stimulation. Unlike SII, however, LEF-5 did not appear to enable RNA polymerase to escape from intrinsic pause sites. Furthermore, LEF-5 did not increase transcription in the presence of small DNA-binding ligands that inhibit elongation in other systems or viral DNA-binding proteins which inhibit the baculovirus RNA polymerase. Exonuclease activity assays revealed that baculovirus RNA polymerase has an intrinsic exonuclease activity, but this was not increased by the addition of LEF-5. Initiation assays and elongation assays using heparin to prevent reinitiation indicated that LEF-5 was active only in the absence of heparin. Taken together, these results suggest that LEF-5 functions as an initiation factor and not as an elongation factor.

* Corresponding author. Mailing address: Department of Biochemistry, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128. Phone: (979) 845-7556. Fax: (979) 845-9274. E-mail: lguarino{at}tamu.edu.

Journal of Virology, December 2002, p. 12663-12675, Vol. 76, No. 24
0022-538X/02/$04.00+0     DOI: 10.1128/JVI.76.24.12663-12675.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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